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Duvalia

This article is about the milkweed genus. For the legume genus, see Hypocalyptus.

Duvalia is a succulent plant genus in the subfamily Asclepiadoideae, in the family Apocynaceae (dogbane).

Duvalia
Duvalia corderoyi
Scientific classification Edit this classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Eudicots
Clade: Asterids
Order: Gentianales
Family: Apocynaceae
Subfamily: Asclepiadoideae
Tribe: Ceropegieae
Genus: Duvalia
Haw. 1812 not Bonpland 1813 nor Nees 1818

The genus was first described in 1812, named after the French physician and botanist Henri-Auguste Duval (1777-1814).[1]

Description

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The rare Duvalia parviflora has smooth "potato-shaped" stems and tiny, cream-coloured flowers.
 
Duvalia elegans, the type species of the genus, showing its wider, triangular flower lobes.
 
The hairy flowers of Duvalia vestita (Duvalia caespitosa subsp. vestita).
 
Duvalia caespitosa, one of the commonest and most widespread species, from the west of South Africa

Vegetative

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The Duvalia species are succulent, perennial plants with low, planar growth. The stems are clavate, cylindrical to spherical, in cross-section four-, five-or six-edged, and to about 10 inches long. They can range from green, gray to mottled reddish in color.

The stems of some species, such as the rounded Duvalia parviflora, are distinctive, and these species can be identified even when not in flower. However the stems are very variable, and most Duvalia species can only be distinguished from each other when the flower is seen.

The stems are superficially very similar to those of the related genus Piaranthus, and the two are often confused when not in flower. In cross-section, Duvalia stems are sometimes five or six sided (Piaranthus stems are always four-sided in cross-section). To accurately distinguish them however, it is necessary to examine the flowers.

Floral

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The distinctive flowers are on long, bare stalks, which grow from the base of the stems.

Each flower has five thin, elongated petal-like lobes, radiating in a star-shape, from a central raised disk or annulus.

The colour of most species flowers is shades of reddish brown, except for those of the rare Duvalia parviflora which are cream-coloured. The hermaphroditic flowers measure 1–5 cm in diameter, and have five parts. The crown is yellow ocher, brown, red to dark purple. The five corolla lobes are flat or folded along the middle nerve.

Distribution

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It occurs in southern Africa. The majority of the species are restricted to the western part of South Africa & Namibia, with the greatest number of species occurring in the Great Karoo region, on the edge of the winter rainfall area. Only one species, Duvalia polita extends further east, and as far north into tropical Africa as Malawi and Zambia.[2][3]

Four species, occurring on the other side of the continent on the verges of the Red Sea, were formerly included in the genus Duvalia. However phylogenetic studies have shown them to be relatively unrelated to the rest of the genus, and more closely related to genus Ballyanthus Bruyns.[4]

Species[5]
  1. Duvalia anemoniflora (Deflers) R.A. Dyer & Lavranos - Arabia
  2. Duvalia angustiloba N.E.Br. - South Africa
  3. Duvalia caespitosa (Masson) Haw. - South Africa
  4. Duvalia corderoyi (Hook.f.) N.E.Br. - South Africa
  5. Duvalia eilensis Lavranos - Somalia
  6. Duvalia elegans (Masson) Haw. - Cape Province
  7. Duvalia galgallensis Lavranos - Somalia
  8. Duvalia gracilis Meve - Cape Province
  9. Duvalia immaculata (C.A.Lückh.) M.B.Bayer ex L.C.Leach - South Africa
  10. Duvalia maculata N.E.Br. - South Africa
  11. Duvalia modesta N.E.Br. - South Africa
  12. Duvalia parviflora N.E.Br. - Cape Province
  13. Duvalia pillansii N.E.Br. - Cape Province
  14. Duvalia polita N.E.Br. - South Africa
  15. Duvalia pubescens N.E.Br. - Cape Province
  16. Duvalia somalensis Lavranos - Somalia
  17. Duvalia sulcata N.E.Br. - Arabia
  18. Duvalia velutina Lavranos - Saudi Arabia
  19. Duvalia vestita Meve - Cape Province
formerly included[5]

transferred to Mannia

References

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Wikimedia Commons has media related to Duvalia (Apocynaceae).
  1. ^ Haworth, Adrian Hardy. 1812. Synopsis Plantarum Succulentarum: cum descriptionibus, synonymis, locis, observationibus anglicanis, culturaque 44.
  2. ^ Tropicos Duvalia
  3. ^ Gibbs Russell, G. E., W. G. M. Welman, E. Retief, K. L. Immelman, G. Germishuizen, B. J. Pienaar, M. Van Wyk & A. Nicholas. 1987. List of species of southern African plants. Memoirs of the Botanical Survey of South Africa 2(1–2): 1–152(pt. 1), 1–270(pt. 2).
  4. ^ P. Bruyns, C. Klak, P. Hanacek: Evolution of the stapeliads (Apocynaceae-Asclepiadoideae) - repeated major radiation across Africa in an Old World group. Molecular Phylogenetics and Evolution. 2014. v. 77, no. 1, p. 251--263. ISSN 1055-7903.
  5. ^ a b The Plant List, Duvalia

Portions of this page were translated from the equivalent page on the German wikipedia accessed July 3, 2012

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